Shielded electron discharge device



. I, 1936. w. KAUTTER ETAL SHIELDED ELECTRON DISCHARGE DEVICE F ile d June 23, 1934 INVENTO'R Patented Dec. 1, 1936 UNITED- STATES PATENT OFFICE SHIELDED ELECTRON DISCHARGE DEVICE Application June 23, 1934, Serial No. 732,034 In Germany July 5, 1933 1 Claim.

Our invention relates to an electron discharge tube having an indirectly heated cathode, more particularly to shielding means in such a. tube for preventing inductive action upon the electrodes in the tube by the alternating voltage used to energize the heater of the cathode.

In radio receiver sets and in amplifiers where the heater voltage is derived directly or by way of series resistances or transformers from a supply line, it is the usual practice to employ tubes having indirectly heated cathodes. These cathodes as a general rule consist of a metallic sleeve having an electron-emissive coating, the sleeve surrounding a ceramic body in the interior of which is embedded a heater element. While the mass or volume of such cathodes is usually so large that the fluctuations of energy (electron emission) due to the alternating voltage supply will not become appreciable or effective to disturb operation of the tube because of the thermal inertia of the cathode, disturbances are caused due to the capacitive coupling of the heater leads and the rest of the electrodes of the tube. For preventing these disturbances the cathode has been extended in the form of a tube thru the press, the heating leads being placed within the tube. However, remedies of this kind have failed of more generaladoption in practice because of the difficulties of manufacture.

It is therefore an object of our invention to provide an electron discharge device having an indirectly heated cathode with a simple and effective means for almost completely shielding the cathode heater leads from the other electrodes of the tube to prevent undesirable coupling.

According to one form of our invention, we provide a shield electrically connected to the metallic cathode and extending transversely of and to the inside wall of the glass bulb or envelope thus dividing the interior of the bulb into two compartments. The electrode leads are so disposed that the heater leads only extend inside one compartment, whereas all of the other leading-in wires extend into the other compartment of the tube. The electrical separation can be extended by means of a metallic mirror or deposit on the inside wall of the glass bulb or envelope and maintained preferably at cathode potential.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claim, but the inven tion itself will best be understood by reference to the following description taken in connection with the accompanying drawing showing a schematic longitudinal cross section of an electron discharge device embodying our invention.

In the drawing a tube l of ceramic material, supports on its outside a metallic tube or sleeve 2, which is coated with an electron-emissive layer. The grid electrode 3, and the plate electrode 4 complete the electrode system. The leads of the last two electrodes as well as the cathode leads are brought in from the outside of the envelope thru the press 5 in the usual manner.

In accordance with our invention a metallic shield 6 is connected to the cathode tube or sleeve 2, and is constructed to extend transversely of and to the wall of the glass envelope I I, thereby dividing the interior of the envelope into two separate spaces or compartments 1 and 8. The heater leads 9 are brought out thru the opposite end of the tube from the press 5. In order that the shielding may be still more effective, the tube is provided on the inside wall of the envelope with a metallic mirror coating or deposit l0 which is kept at cathode potential.

. While we have indicated the preferred embodiment of our invention of which we are now aware and have also indicated only one specific application for-which our invention may be employed, it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claim.

What we claim as new is,

An electron discharge tube having an envelope and a metallic coating on the inside wall of said envelope, an indirectly heated cathode positioned Within said envelope and including a sleeve closed at one end, a heater extending within said sleeve and provided with leads extending thru said envelope, concentric electrodes surrounding said cathode sleeve, leads to said cathode and said concentric electrodes extending thru said envelope in a direction opposite from said heater leads, and a metal shield extending transversely of the envelope into proximity to said envelope and electrically connected to said metallic coating and the open end of said cathode sleeve for dividing said envelope into two shielded compartments, one of said compartments containing the heater leads and the other of said compartments containing the cathode and other electrodes, said metal shield and metallic coating electrostatically shielding said heater leads from the leads to said cathode and other electrodes and from the other electrodes within said envelope.

WOLFGANG KAUTTER. HANS OTTO ROOSENSTEIN. 

